1. Technical Field
Methods for forming dielectric films of capacitors are disclosed wherein a high K oxide monoatomic layer having a high dielectric constant such as SrTiO3 and (Ba,Sr)TiO3 is formed by using an atomic layer deposition having high step coverage to provide sufficient capacitance for high integration of the semiconductor device in case of a capacitor having a high aspect ratio and a geometrically-complicated structure.
2. Description of the Related Art
As the size of a cell decreases due to high integration density, it becomes more difficult to obtain sufficient capacitance which is proportional to the surface area of a storage node.
In particular, in the DRAM wherein a unit cell includes a MOS transistor and a capacitor, a capacitance of the capacitor needs to be increased and an area occupied by the capacitor needs to be decreased to achieve high integration.
Therefore, in order to increase the capacitance of the capacitor which follows the equation (Eoxc3x97Erxc3x97A)/T (where Eo denotes a vacuum dielectric constant, Er denotes a dielectric constant of a dielectric film, A denotes an area of the capacitor and T denotes a thickness of the dielectric film), a method of increasing a surface area of a storage node which is a lower electrode has been proposed.
However, the method for increasing the surface area of the storage node has reached a limit due to the high integration density and process limitations of the semiconductor device.
Recently, a method for forming a capacitor using a dielectric film having a high dielectric constant has been proposed to obtain sufficient capacitance for highly integrated semiconductor devices.
The dielectric film having a high dielectric constant is deposited on the surface of the storage node having a large step difference according to atomic layer deposition. However, when atomic layer deposition is performed to form a dielectric layer from at least two source materials, the composition of the dielectric layer becomes very difficult to control.
A method for controlling the composition of dielectric layers by varying a feed ratio of each source material has been suggested. However, precise control of the feed ratio is almost impossible since the feed ratio is a multiple of the intrinsic deposition rate of each source material.
FIG. 1 is a graph showing a conventional method for controlling the composition of a dielectric layer formed from two source materials and a reaction gas using atomic layer deposition, wherein general variations in the deposition rate relative to the flow rate of the reaction gas is illustrated.
Since the atomic layer deposition is based on adsorption reaction on the surface of a substrate, the deposition rate saturates to a predetermined value when flow rate of the reaction gas reaches a predetermined value.
Here, a and b of FIG. 1 which are the deposition rates at saturation have specific values according to each source material and reaction gas.
In addition, when chemical properties of the source materials and the reaction gas are determined, critical values of the source gas and the reaction gas are fixed to one value to obtain the saturated deposition rate a or b.
Accordingly, when the oxide thin film composed of a material having at least two components is formed according to the atomic layer deposition, a complicated process results wherein the feeding ratio of each source is varied as required to form the oxide thin film having stoichiometric compositions with the saturated deposition rate.
Accordingly, a method for forming a dielectric film of a capacitor is disclosed which has sufficient capacitance for highly integrated semiconductor devices by forming a dielectric film having a high dielectric constant using atomic layer deposition with excellent step coverage.
One disclosed method for forming a multi-component dielectric film comprises: (a) injecting a first source containing a first component into a reaction chamber to be adsorbed on a surface of a substrate; (b) purging residual first source out of the reaction chamber; (c) injecting a mixed gas of Ar and O2 in plasma state into the reaction chamber to react with the first component adsorbed on the substrate; (d) purging by-products and residual gas out of the reaction chamber; (e) injecting a second source containing a second component into the reaction chamber to be adsorbed to the surface of the resulting structure; (f) purging residual second source out of the reaction chamber; (g) injecting a mixed gas of Ar and O2 in plasma state into the reaction chamber to induce oxidation reaction; and (h) purging residual gas and by-products out of the reaction chamber using mixed gas of Ar and O2, wherein the substrate is selected from the group consisting of Si, SiO2, TiN, TiSiN, TiAlN, Ru, Pt, Ir, RuO2, IrO2, and combinations thereof; the purge processes of step (b), (d), (f) and (h) are performed using a vacuum pump; the purge processes of step (b), (d), (f) and (h) are performed using a vacuum pump with an inert gas added thereto; the method further comprises a step of injecting O2 gas into the reaction chamber for 0.1 to 10 seconds during the step (c) and (g), respectively; step (c) and (g) is performed on the condition of maintaining the reaction chamber at a pressure ranges from 0.5 to 5.0 Torr; the O2 gas ratio of the mixed gas of Ar and O2 in plasma state is 20 to 40% in the step (c) and (g), respectively; mixed gas of Ar and O2 in plasma state is generated in the reaction chamber or a remotely generated out of the chamber and then supplied into the reaction chamber; during the step (a) to (h) the substrate is maintained at a temperature ranging from 150 to 300xc2x0 C. and the first source and the second source are injected for a time period ranging from 0.1 to 10 seconds; one of the first source and the second source is Sr and the other is Ti; the Sr source is selected from the group consisting of Sr(THD)2, Sr(METHD)2, and solutions thereof; the Ti source is selected from the group consisting of Ti(i-OC3H7)4, Ti(n-OC4H9)4, Ti(t-OC4H7)4, Ti(OC2H5)4, Ti(OCH3)4, Ti(n-OC3H7)4 and combinations thereof; the Sr source and the Ti source are injected for a time period ranging from 0.1 to 10 seconds in the processes (a) and (e), respectively; the purge processes of step (b), (d), (f) and (h) are performed using a vacuum pump; the purge processes of step (b), (d), (f) and (h) are performed using a vacuum pump with an inert gas added thereto; the step (c) and (g) is performed on the condition of: maintaining the pressure of the reaction chamber ranging from 0.5 to 5.0 Torr; injecting O2 for a time period ranging from 0.1 to 10 seconds; and injecting a mixed gas of Ar and O2; the mixed gas of Ar and O2 in plasma state is generated in the reaction chamber or a remotely generated and then supplied into the reaction chamber; the O2 gas ratio of the mixed gas of Ar and O2 in plasma state is 20 to 40%; the substrate is maintained at a temperature ranging from 150 to 300xc2x0 C. and the first source and the second source are injected for a time period ranging from 0.1 to 10 seconds in the step (a) to (h), respectively; and the first source is a cocktail source of Sr/Ti and the second source is Ti source.
The principles of the disclosed methods will now be explained.
The disclosed method controls compositions of dielectric layers by using differences of reaction rates between reaction gas and each source material while using conventional atomic layer deposition having a surface chemical reaction property of a monoatomic layer.
For example, when SrTiO thin film is formed according to atomic layer deposition using Sr source and Ti source, Ar/O2 mixed gas is activated in a remote plasma device and injected into a reaction chamber as an oxidation source, which allow precise control of compositions of SrTiO3 thin film without changing a feeding ratio of Si source and Ti source which are absorbed by using oxidation reaction differences between each source and Ar/O2.
Here, Sr source is selected from the group consisting of xcex2-Diketonate group Ligand containing Sr(THD)2 or Sr(METHD)2, solutions thereof, and Ti source is an alkoxide group material selected from the group consisting of Ti(i-OC3H7)4, Ti(n-OC4H9)4, Ti(t-OC4H7)4, Ti(OC2H5)4, Ti(OCH3)4, Ti(n-OC3H7)4 and combinations thereof.